Small semiconductor-scale devices such as capacitors are widely used in electronics such as personal electronics. These devices may be used as pressure transducers. For example, the devices can be used as microphones, such as for recording or playing sound. They may be used as motion detectors, functioning as accelerometers and/or gyroscopes. Other uses are possible. As market demand for personal electronics grows, manufacturers seek to benefit from devices of reduced size and decreased cost so that they may create improved personal electronics.
U.S. Pat. No. 7,539,003 provides capacitive sensors with single crystal silicon on all key stress points. Isolating trenches are formed by trench and refill forming dielectrically isolated conductive silicon electrodes for drive, sense and guards, as illustrated in FIG. 1A. The pressure port is opposed to the electrical wire bond pads for ease of packaging. Dual-axis accelerometers measuring in-plane acceleration and out-of-plane acceleration are also described. A third axis in plane is provided by duplicating and rotating the accelerometer 90 degrees about its out-of-plane axis.
As illustrated in FIG. 1A, one of the approaches in U.S. Pat. No. 7,539,003 relies on devices formed using an undesirable single-material dielectric trench 100 configuration. The trench passes through a semiconductor 101 and has two contacts 102. It is difficult to manufacture, at least because it is difficult to deposit fill as shown.